Water or hydrocarbons (e.g. oil and natural gas) in a water- or hydrocarbon-bearing zone can be reached by drilling a wellbore into the earth, either on land or under the sea, which penetrates into the aquifer or hydrocarbon-bearing formation. Such a wellbore can be used to produce water or hydrocarbons or as an injector well to inject fluid, e.g. water or gas, to drive the relevant fluids into a production wellbore. Typically such a wellbore must be drilled deep into the earth. Usually the greater the depth of the well, the higher the natural temperature of the formation.
After drilling an open hole, the next step is referred to as “completing” the wellbore. A wellbore is sometimes completed openhole, that is, without cemented casing in place adjacent to the producing formations. More typically, however, as part of the well completion process, a metal pipe, known as “casing” is positioned and cemented into place in the openhole. Where the wellbore penetrates into a hydrocarbon- or water-bearing zone of a subterranean formation, the casing can be perforated to allow fluid communication between the zone and the wellbore. A zone of a wellbore that penetrates a hydrocarbon-bearing zone that is capable of producing hydrocarbons is referred to as “production zone”. The casing also enables separation or isolation of one or more production zones of the wellbore, for example, by using downhole tools such as packers or plugs, or by using other techniques, such as forming sand plugs or placing cement in the perforations.
Whether the wellbore is openhole or cased, various procedures are often employed to complete the wellbore in preparation for production of hydrocarbons or recovery of water. For example, one common procedure is gravel packing to help prevent sand and fines from flowing with the hydrocarbon produced into the wellbore. Another example of a common procedure to stimulate the flow of hydrocarbon production from the hydrocarbon-bearing zones is hydraulic fracturing of a formation. This procedure is often referred to as “fracking” to provide improved flow path for hydrocarbons to flow from the hydrocarbon-bearing formation to the wellbore.
After a well has been completed and placed into production, from time to time it is helpful to workover a well by performing major maintenance or remedial treatments. Workover includes the stimulation and remediation of a well to help restore, prolong, or enhance the production of hydrocarbons or the recovery of water. During well servicing or workover, various treatment procedures may be used, including for example, gravel packing or hydraulic fracturing.
All these procedures, from drilling the wellbore, to cementing, to completion, to workover, employ appropriate fluids. During the initial drilling and construction of the wellbore, the fluids are often referred to as treatment fluids, completion fluids, or workover fluids. As used herein, “treatment fluid” includes any appropriate fluid to be introduced into a wellbore, whether during drilling, completion, servicing, workover or any other such stage. These treatment fluids, often also called “servicing fluid” typically are water-based fluids comprising a rheology modifier and/or a fluid loss modifier.
A wide variety of water-soluble or water-swellable polymers, such as cellulose ethers, starches, guar gums, xanthan gums, and synthetic polymers and copolymers of acrylamide, acrylic acid, acrylonitrile, and 2-acrylamido-2-methylpropanesulfonic acid are used in water-based servicing fluids.
U.S. Pat. No. 4,784,693 discloses the use of hydrophobically modified hydroxyethyl cellulose having 2-4 weight percent hydrophobic substitution, an MS (hydroxyethoxyl) substitution of 1.5-4 and a viscosity of 300-500 cps, measured as a 1 wt.-% aqueous solution, for use in oil drillings.
U.S. Pat. No. 4,529,523 discloses the use of hydrophobically modified cellulose ethers, such as hydroxyethyl cellulose having about 1 weight percent hydrophobic substitution, an MS (hydroxyethoxyl) substitution of 2.5 and molecular weights of 50,000-1,000,000, preferably about 150,000-800,000, as water flooding medium.
U.S. Pat. No. 4,228,277 discloses a nonionic hydroxyethyl or hydroxypropyl cellulose ether being substituted with a long chain alkyl radical having 10 to 24 carbon atoms in an amount between about 0.2 weight percent and the amount which renders the cellulose ether less than 1% by weight soluble in water. The products are said to exhibit improved viscosifying effect compared to their unmodified cellulose ether counterparts.
U.S. Pat. No. 4,892,589 discloses a cementing composition comprising hydraulic cement and, as a fluid loss agent, water-soluble, non-ionic hydrophobically modified hydroxyethyl cellulose.
U.S. Pat. No. 5,407,919 discloses a double-substituted, cationic water-soluble cellulose ether with hydrophobe-modification with alkyl groups of 8 to 18 carbon atoms and with a cationic substitution with a trimethyl- or triethylammonium group. The molecular weight of this cationic hydrophobe-modified hydroxyethyl cellulose is described as 10,000 to 500,000 Daltons. The cationic hydrophobe-modified hydroxyethyl cellulose polymers described in this patent are useful in cosmetic, personal care, and pharmaceutical applications.
US patent application 2007/0031362 A1 discloses a double-substituted, cationic water-soluble cellulose ether with hydrophobe-modification with alkyl groups of 8 to 18 carbon atoms and with the cationic substitution with a trimethyl- or triethylammonium group. The degree of polymerization of this cationic hydrophobe-modified hydroxyethyl cellulose is described as 4,000 to 10,000. The cationic hydrophobe-modified hydroxyethyl cellulose polymers described in this patent are useful in cosmetic, personal care, and pharmaceutical applications.
As the world's demand for hydrocarbons such as petroleum and natural gas continues to grow while known reserves are depleted, wells of increased depth are drilled. The deeper the drilled well is, the higher generally is the temperature of the subterranean formation. Unfortunately, many of the known water-soluble or water-swellable polymers used as rheology modifiers and/or a fluid loss modifiers used in water-based servicing fluids exhibit a reversible loss of viscosity at elevated temperatures, also known as thermal thinning. However, in many end-use applications, such as water, petroleum and natural gas recovery (e.g., drilling fluids, workover fluids, or completion fluids, cementing wells, hydraulic fracturing, and enhanced oil recovery), construction (e.g., concrete pumping and casting, self-leveling cement, cementing geothermal wells, extruded concrete panels), full-depth road reclamation, ceramics (e.g., as green strength additive), metal working and cutting fluids, thermal thinning is highly undesirable. One specific unmet need in the hydrocarbon recovery industry is for water-soluble polymers with improved high temperature viscosity retention down-hole. Temperatures down-hole can exceed 250° F. (120° C.), and most oil-field applications of water-soluble polymers depend on the solid suspending efficiency of these polymer solutions at these elevated temperatures. Accordingly, it would be desirable to find new cellulose ethers which exhibit a reduced degree of thermal thinning and thus would be more efficient thickeners at elevated temperatures.